The sperm structure that releases digestive enzymes upon contact with the zona pellucida, clearing a path to the oocyte, undergoes the:

1. After capacitation, a sperm still must physically breach the corona radiata and zona pellucida. 2. Upon binding to zona pellucida receptors, a specific enzyme-releasing event is triggered in the sperm's cap structure. 3. This event is called the acrosomal reaction. 4. This is distinct from the cortical reaction, which is the oocyte's own block against polyspermy, so that option is ruled out. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 28 "Development and Inheritance", p.1320-1321 §Contact Between Sperm and Oocyte_